1. Technical Field of the Invention
The present invention relates to an optical disc apparatus, and more particularly to a technology for recording information onto and reproducing information from a plurality of recording layers on an optical disc.
2. Description of the Related Art
There is a strong market need for increasing the recording speed, that is, reducing the recording time, of DVD±R discs and other optical discs having two recording layers. Conventionally, such a market need has been satisfied by increasing the rotation speed of an optical disc. However, when the rotation speed is increased, the focus servo and tracking servo become unstable due to the distortion possessed by the optical disc, thereby deteriorating the recording quality. Therefore, when a servo signal distortion is detected, the rotation speed of the optical disc is decreased to stabilize the focus servo and tracking servo with a view toward stabilizing the recording quality.
FIGS. 11A and 11B illustrate a conventional technology for an optical disc apparatus that records information onto or reproduces information from a double-layer optical disc. In the illustrated example, when a recording operation is performed from inner tracks to outer tracks of a first recording layer (first layer) and performed from outer tracks to inner tracks of a second recording layer (second layer), the recording operation in an inner first zone of the first layer is performed at a recording speed of v1′; the recording operation in the next second zone, which begins at point P, is performed at a recording speed of v2′; and the recording operation in the next third zone, which begins at point Q, is performed at a recording speed of v3′. In the second layer, the recording operation in a third zone of the second layer, which is in the same disc radial position as the third zone of the first layer, is performed at a recording speed of v3′; the recording operation in a second zone of the second layer, which is in the same disc radial position as the second zone of the first layer, is performed at a recording speed of v2′; and the recording operation in a first zone of the second layer, which is in the same disc radial position as the first zone of the first layer, is performed at a recording speed of v1′. If no distortion is detected in a servo signal, the recording operations in the first, second, and third zones of both the first and second layers are performed at recording speeds v1′, v2′, and v3′, respectively. However, if a distortion is detected in the servo signal, the recording operations are performed as indicated in FIGS. 11A and 11B. FIG. 11A shows a case where a distortion is detected in the servo signal at point R of the third zone of the first layer. FIG. 11B shows a case where a distortion is detected in the servo signal at point S of the second zone of the first layer. In the case indicated in FIG. 11A, the recording speed is decreased at point R from v3′ to v2′, and the recording speed v2′ is maintained until the recording operation for the second layer is terminated. Even in the third zone of the second layer, the recording speed does not revert to v3′. Further, in the case indicated in FIG. 11A, the recording speed is decreased at point S from v2′ to v1′, and the recording speed v1′ is maintained until the recording operation for the second layer is terminated. Even in the third zone of the first layer and in the third zone of the second layer, the recording speed does not revert to v3′. Even in the second zone of the second layer, the recording speed does not revert to v2′.
Another conventional technology is such that the recording speed is constantly lowered for outer tracks of the disc to cope with a distortion in the outer tracks.
Other conventional technologies related to the present invention are disclosed, for instance, by Japanese Patents JP-A No. 62945/2004 and JP-A No. 109822/2002. To record data in a stable manner even when the more outer track is, the lower quality is due to partial distortion of an optical disc, the technology disclosed by Japanese Patent JP-A No. 62945/2004 monitors high-frequency components of a tracking error signal and focusing error signal while data is recorded onto or reproduced from an optical disc at a high speed. If an eccentric acceleration or runout acceleration greater than a predetermined threshold value is detected, this technology decreases the linear velocity particularly for outer tracks at a predetermined ratio to lower the frequencies for eccentric acceleration and runout acceleration, and performs a recording or reproducing operation with the responses of the tracking servo and focusing servo improved. The technology disclosed by Japanese Patent JP-A No. 109822/2002 prevents a lack of read/write margin due to high-speed optical disc rotation in a storage apparatus using an optical disc. To maintain the focusing servo and tracking servo stable, this technology decreases the rotation speed of a spindle motor when the read/write margin is smaller than a first predetermined value or when tracking/focusing servo abnormality occurs more frequently than a first predetermined frequency. On the other hand, when the read/write margin is greater than a second predetermined value or when the tracking/focusing servo abnormality occurs less frequently than a second predetermined frequency, this technology increases the rotation speed of the spindle motor.